Biotin biosynthetic genes having biotin synthase activity

ABSTRACT

The present invention relates to the production process of biotin by fermentation using a genetically engineered microorganism, and DNA sequences and vectors to be used in such process.

This application is a divisional of U.S. application Ser. No. 10/033,078, filed Dec. 27, 2001, now U.S. Pat. No. 6,723,544, which is a divisional of U.S. application Ser. No. 09/594,185, filed Jun. 14, 2000, now U.S. Pat. No. 6,365,388, which is a divisional of U.S. application Ser. No. 08/935,263, filed Sep. 22, 1997, now U.S. Pat. No. 6,117,669.

BACKGROUND OF THE INVENTION

The present invention relates to the production process of biotin by fermentation using a genetically engineered organism.

Biotin is one of the essential vitamins for nutrition of animals, plants, and microorganisms, and very important as medicine or food additives.

Biotin biosynthesis of Escherichia coli has been studied well, and it has been clarified that biotin is synthesized from pimelyl CoA via 7 keto-8-amino pelargonic acid (KAPA), 7,8-diamino pelargonic acid (DAPA) and desthiobiotin (DTB) [Escherichia coli and Salmonella typhimurium, Cellular and Molecular Biology, 544, (1987)]. The analysis of genetic information involved in the biosynthesis of biotin has been advanced on Escherichia coli [J. Biol. Chem., 263, 19577, (1988)] and Bacillus sphaericus (U.S. Pat. No. 5,096,823). At least four enzymes are known to be involved in this biosynthetic pathway. These four enzymes are encoded by the bioA, bioB, bioD and bioF genes. The bioF gene codes for KAPA synthetase which catalyzes the conversion of pimelyl CoA to KAPA. The bioA gene codes for DAPA aminotransferase which converts KAPA to DAPA. The bioD gene codes for DTB synthetase which converts DAPA to DTB. The bioB gene codes for biotin synthase which converts DTB to biotin. It has been also reported that the bioC and bioH genes are involved in the synthesis of pimelyl CoA in Escherichia coli.

There are many studies on fermentative production of biotin. Escherichia coli (Japanese Patent Kokai No. 149091/1986 and Japanese Patent Kokai No. 155081/1987), Bacillus sphaericus (Japanese Patent Kokai No. 180174/1991), Serratia marcescens (Japanese Patent Kokai No. 27980/1990) and Brevibacterium flavum (Japanese Patent Kokai No. 240489/1991) have been used. But these processes have not yet been suitable for use in an industrial production process because of a low productivity. Moreover, large amounts of DTB, a biotin precursor, accumulates in the fermentation of these bacteria. Therefore, it has been assumed that the last step of the biotin biosynthetic pathway, from DTB to biotin, is a rate limiting step.

On the other hand, it was found that a bacterial strain belonging to the genus Kurthia produces DTB and small amounts of biotin. Also mutants which produce much larger amounts of biotin were derived from wild type strains of the genus Kurthia by selection for resistance to biotin antimetabolites acidomycin (ACM), 5-(2-thienyl)-valeric acid (TVA) and alpha-methyl desthiobiotin (MeDTB). However, in view of the still low biotin titers it is desirable to apply genetic engineering to improve the biotin productivity of such mutants.

SUMMARY OF THE INVENTION

The present invention relates therefore to the chromosomal DNA fragments carrying the genes involved in the biotin biosynthesis of Kurthia sp. The isolated chromosomal DNA fragments carry 8 genes, the bioA, bioB, bioC, bioD, bioF, bioFII, bioH and bioHII genes, and transcriptional regulatory sequences. The bioFII gene codes for an isozyme of the bioF gene product. The bioHII gene codes for an isozyme of the bioH gene product.

The present invention further relates to Kurthia sp. strains in which at least one gene involved in biotin biosynthesis is amplified, and also to the production process of biotin by this genetically engineered Kurthia sp. strain.

Although the DNA fragment mentioned above may be of various origins, it is preferable to use the strains belonging to the genus Kurthia. Specific examples of such strains include, for example, Kurthia sp. 538-6 (DSM No. 9454) and its mutant strains by selection for resistance to biotin antimetabolites such as Kurthia sp. 538-KA26 (DSM No. 10609).

BRIEF DESCRIPTION OF THE FIGURES

Before the present invention is explained in more detail by referring to the following examples a short description of the enclosed Figures is given:

FIG. 1: Restriction maps of pKB100, pKB200 and pKB300.

FIG. 2: Structure of pKB100.

FIG. 3: Structure of pKB200.

FIG. 4: Restriction maps and complementation results of pKH100, pKH101 and pKH102.

FIG. 5: Structure of pKH100.

FIG. 6: Restriction maps of pKC100, pKC101 and pKC102.

FIG. 7: Structure of pKC100.

FIG. 8: Structures of derived plasmids from pKB100, pKB200 and pKB300.

FIG. 9: Gene organizations of the gene clusters involved in biotin biosynthesis of Kurthia sp. 538-KA26.

FIG. 10: Nucleotide sequence between the ORF1 and ORF2 genes of Kurthia sp. 538-KA26.

FIG. 11: Nucleotide sequence of the promoter region of the bioH gene cluster.

FIG. 12: Nucleotide sequence of the promoter region of the bioFII gene cluster.

FIG. 13: Construction of the shuttle vector pYK1.

FIG. 14: Construction of the bioB expression plasmid pYK114.

DETAILED DESCRIPTION OF THE INVENTION

Generally speaking the present invention is directed to DNA molecules comprising polynucleotides encoding polypeptides represented by SEQ ID Nos. 2, 4, 6, 8, 10, 12, 14 or 16, and functional derivatives of these polypeptides which contain addition, insertion, deletion and/or substitution of one or more amino acid residue(s), and to DNA molecules comprising polynucleotides which hybridize under stringent hybridizing conditions to polynucleotides which encode such polypeptides and functional derivatives. The invention is also directed to vectors comprising one or more such DNA sequences, for example, a vector wherein said DNA sequences are functionally linked to promoter sequence(s). The invention is further directed to biotin-expressing cells, said cells having been transformed by one or more DNA sequences or vector(s) as defined above, and a process for the production of biotin which comprises cultivating a biotin-expressing cell as defined above in a culture medium to express biotin into the culture medium, and isolating the resulting biotin from the culture medium by methods known in the art. Any conventional culture medium and culturing conditions may be used in accordance with the invention. Preferably, such a process is carried out wherein the cultivation is effected from 1 to 10 days, preferably from 2 to 7 days, at a pH from 5 to 9, preferably from 6 to 8, and a temperature range from 10 to 45° C., preferably from 25 to 30° C.

Finally, the present invention is also directed to a process for the preparation of pharmaceutical, food or feed compositions characterized therein that biotin obtained by such processes is mixed with one or more generally used additives with which a man skilled in the art is familiar.

The DNA molecules of the invention may be produced by any conventional means, such as by the techniques of genetic engineering and automated gene synthesis known in the art.

A detailed method for isolation of DNA fragments carrying the genes coding for the enzymes involved in the biotin biosynthesis from these bacterial strains is described below.

Therefore, DNA can be extracted from Kurthia sp. 538-KA26 by the known phenol method. Such DNA is then partially digested by Sau3AI and ligated with pBR322 digested by BamHI to construct a genomic library of Kurthia sp. 538-KA26.

Biotin auxotrophic mutants which lack the biosynthetic ability to produce biotin are transformed with the genomic library obtained above, and transformants showing biotin prototrophy are selected. The selected transformants have the genomic DNA fragments complementing deficient genes in the biotin auxotrophic mutants. As biotin auxotrophic mutants, Escherichia coli R875 (bioB⁻), R877 (bioD⁻), BM7086 (bioH⁻) and R878 (bioC⁻) (J. Bacteriol., 112, 830-839, (1972) and J. Bacteriol., 143, 789-800, (1980) can be used. The transformation of such Escherichia coli strains can be carried out according to a conventional method such as the competent cell method [Molecular Cloning, Cold Spring Harbor Laboratory Press, 252, (1982)].

In the present invention, a hybrid plasmid which complements the bioB deficient mutant of Escherichia coli was obtained in the manner described above. The obtained hybrid plasmid is named pKB100. The pKB100 corresponds to plasmid pBR322 carrying a 5.58 Kb of a genomic DNA fragment from Kurthia sp. 538-KA26, and its restriction cleavage map is shown in FIGS. 1 and 2.

The hybrid plasmid named pKB200 which complements the bioD deficient mutant of Escherichia coli was also obtained as described above. The pKB200 corresponds to plasmid pBR322 carrying a 7.87 Kb of genomic DNA fragment from Kurthia sp. 538-KA26, and its restriction cleavage map is shown in FIGS. 1 and 3. The genomic DNA fragment in pKB200 completely overlapps with the inserted fragment of the pKB100 and carries the bioF, bioB, bioD, ORF1 and ORF2 genes and a part of the bioA gene of Kurthia sp. 538-KA26 as shown in FIG. 9-A.

The complete bioA gene of Kurthia sp. 538-KA26 can be isolated by conventional methods, such as colony hybridization using a part of the genomic DNA fragment in pKB200 as a probe. The whole DNA of Kurthia sp. 538-KA26 is digested with a restriction enzyme such as HindIII and ligated with a plasmid vector cleaved by the same restriction enzyme. Then, Escherichia coli is transformed with the hybrid plasmids carrying genomic DNA fragments of Kurthia sp. 538-KA26 to construct a genomic library. As a vector and Escherichia coli strain, the pUC19 [Takara Shuzo Co.(Higashiiru, Higashinotohin, Shijodohri, Shirnogyo-ku, Kyoto-shi, Japan)] and Escherichia coli JM109 (Takara Shuzo Co.) can be used, respectively.

The hybrid plasmid named pKB300 carrying a 8.44 Kb genomic DNA fragment from Kurthia sp. 538-KA26 was obtained by colony hybridization and its restriction cleavage map is shown in FIG. 1. The genomic DNA fragment in the pKB300 carries two gene clusters involved in the biotin biosynthesis of Kurthia sp. 538-KA26 as shown in FIG. 9-A. One cluster consists of the ORF1, bioD and bioA genes. Another cluster consists of the ORF2, bioF and bioB genes. The nucleotide sequences of the bioD and bioA genes are shown in SEQ ID No. 1 and SEQ ID NO: 3, respectively. The predicted amino acid sequences of the bioD and bioA gene products are shown in SEQ ID NO: 2 and SEQ ID NO: 4, respectively. The bioD gene codes for a polypeptide of 236 amino acid residues with a molecular weight of 26,642. The bioA gene codes for a polypeptide of 460 amino acid residues with a molecular weight of 51,731. The ORF1 gene codes for a polypeptide of 194 amino acid residues with a molecular weight of 21,516, but the biological function of this gene product is unknown.

The nucleotide sequences of the bioF and bioB genes are shown in SEQ ID NO: 5 and SEQ ID NO: 7, respectively. The predicted amino acid sequences of the bioF and bioB gene products are SEQ ID NO: 6 and SEQ ID NO: 8, respectively. The bioF gene codes for a polypeptide of 387 amino acid residues with a molecular weight of 42,619. The bioB gene codes for a polypeptide of 338 amino acid residues with a molecular weight of 37,438. The ORF2 gene codes for a polypeptide of 63 amino acid residues with a molecular weight of 7,447, but the biological function of this gene product is unknown. Inverted repeat sequences which are transcriptional terminator signals are found downstream of the bioA and bioB genes. As shown in FIG. 10, two transcriptional promoter sequences which initiate transcriptions in both directions are found between the ORF1 and ORF2 genes. Furthermore, there are two inverted repeat sequences named Box1 and Box2 involved in the negative control of the transcriptions between each promoter sequence and each translational start codon.

In addition, two hybrid plasmids which complement the biotin auxotrophic mutants of Escherichia coli were obtained in the manner described above. The hybrid plasmid named pKH100 complements the bioH deficient mutant, and the hybrid plasmid named pKC100 the bioC mutant. pKH100 (FIGS. 4 and 5) has a 1.91 Kb genomic DNA fragment from Kurthia sp. 538-KA26 carrying a gene cluster consisting of the bioH and ORF3 genes as shown in FIG. 9-B. The nucleotide sequence of the bioH gene and the predicted amino acid sequence of this gene product are shown in SEQ ID NO: 9 and SEQ ID NO: 10, respectively. The bioH gene codes for a polypeptide of 267 amino acid residues with a molecular weight of 29,423. The ORF3 gene codes for a polypeptide of 86 amino acid residues with a molecular weight of 9,955, but the biological function of this gene product is unknown. A promoter sequence is found upstream of the bioH gene as shown in FIG. 11, and there is an inverted repeat sequence which is the transcriptional terminator downstream of the ORF3 genes. Since the promoter region has no inverted sequence such as Box1 and Box2, it is expected that the expressions of these genes are not regulated.

On the other hand, pKC100 carries a 6.76 Kb genomic DNA fragment from Kurthia sp. 538-KA26 as shown in FIGS. 6 and 7. The genomic DNA fragment in pKC100 carries a gene cluster consisting of the bioFII, bioHII and bioC genes as shown in FIG. 9-C. The bioHII and bioFII genes are genes for isozymes of the bioH and bioF genes, respectively, because the bioHII and bioFII genes complement the bioH deficient and the bioF deficient mutants of Escherichia coli, respectively. The nucleotide sequences of the bioFII, bioHII and bioC genes are shown in SEQ ID NO: 11, SEQ ID NO: 13 and SEQ ID NO: 15, respectively. The predicted amino acid sequences of the bioFII, bioHII and bioC gene products are shown in SEQ ID NO: 12, SEQ ID NO: 14 and SEQ ID NO: 16, respectively. The bioFII gene codes for a polypeptide of 398 amino acid residues with a molecular weight of 44,776. The bioHII gene codes for a polypeptide of 248 amino acid residues with a molecular weight of 28,629. The bioC gene codes for a polypeptide of 276 amino acid residues with a molecular weight of 31,599. A promoter sequence is found upstream of the bioFII gene, and there is an inverted repeat sequence named Box3 in the promoter region as shown in FIG. 12. The transcription of these genes terminates at an inverted repeat sequence existing downstream of the bioC gene. Since the nucleotide sequence of Box3 is significantly similar to those of Box1 and Box2. expressions of these genes is estimated to be regulated similarly to the bioA and bioB gene clusters.

Needless to say, the nucleotide sequences and amino acid sequences of the genes isolated above are artificially changed in some cases, e.g., the initiation codon GTG or TTG may be converted into an ATG codon.

Therefore the present invention is also directed to functional derivatives of the polypeptides of the present case. Such functional derivatives are defined on the basis of the amino acid sequence of the present invention by addition, insertion, deletion and/or substitution of one or more amino acid residues of such sequences wherein such derivatives still have the same type of enzymatic activity as the corresponding polypeptides of the present invention. Such activities can be measured by any assays known in the art or specifically described herein. Such functional derivatives can be made either by chemical peptide synthesis known in the art or by recombinant means on the basis of the DNA sequences as disclosed herein by methods known in the state of the art, such as, e.g., that disclosed by Sambrook et al. (Molecular Cloning, Cold Spring Harbour Laboratory Press, New York, USA, second edition 1989). Amino acid exchanges in proteins and peptides which do not generally alter the activity of such molecules are known in the state of the art and are described, for example, by H. Neurath and R. L. Hill in “The Proteins” (Academix Press, New York, 1979, see especially FIG. 6, page 14). The most commonly occurring exchanges are: Ala/Ser, Val/Ile, Asp/Glu, Thr/Ser, Ala/Gly, Ala/Thr, Ser/Asn, Ala/Val, Ser/Gly, Thy/Phe, Ala/Pro, Lys/Arg, Asp/Asn, Leu/Ile, Leu/Val, Ala/Glu, Asp/Gly as well as the reverse.

Furthermore the present invention is not only directed to the DNA sequences as disclosed e.g., in the sequence listing as well as their complementary strands, but also to those which include these sequences, DNA sequences which hybridize under Standard Conditions with such sequences or fragments thereof and DNA sequences, which because of the degeneration of the genetic code, do not hybridize under Standard Conditions with such sequences but which code for polypeptides having exactly the same amino acid sequence.

“Standard Conditions” for hybridization mean in this context the conditions which are generally used by a man skilled in the art to detect specific hybridization signals and which are described, e.g., by Sambrook et al., (s.a.) or preferably so-called stringent hybridization and non-stringent washing conditions, or more preferably so-called stringent hybridization and stringent washing conditions a man skilled in the art is familiar with and which are described, e.g., in Sambrook et al. (s.a.). For purposes of the present invention, stringent hybridization conditions are carried out by hybridizing and washing in 0.2×SSC at about 65° C.

DNA sequences which are derived from the DNA sequences of the present invention either because they hybridize with such DNA sequences (see above) or can be constructed by the polymerase chain reaction by using primers designed on the basis of such DNA sequences can be prepared either as indicated namely by the PCR reaction, or by site directed mutagenesis [see e.g., Smith, Ann. Rev. Genet. 19, 423 (1985)] or synthetically as decribed, e.g., in EP 747 483 or by the usual methods of Molecular Cloning as described, e.g., in Sambrook et al. (s.a.).

As a host strain for the expression and/or amplification of the DNA sequences of the present invention, any microorganism may be used, e.g., those identified in EP 635 572, but it is preferable to use the strains belonging to the genus Kurthia, especially Kurthia sp. 538-6 (DSM No. 9454) and Kurthia sp. 538-51F9 (DSM No. 10610).

In order to obtain a transformant with a high biotin productivity, the DNA sequences of the present invention are used under the control of a promoter which is effective in such host cells. The DNA sequences of the present invention can be introduced into the host cell by transformation with a plasmid carrying such DNA sequences or by integration into the chromosome of the host cell.

When Kurthia sp. 538-51F9 is used as the host cell, Kurthia sp. 538-51F9 may be transformed with a hybrid plasmid carrying at least one gene involved in biotin biosynthesis isolated above from a Kurthia sp. strain. As a vector plasmid for the hybrid plasmid, pUB110 [J. Bacteriol., 154, 1184-1194, (1983)], pHP13 (Mol. Gen. Genet., 209, 335-342, 1987), or other plasmids comprising the origin of replication functioning in Kurthia sp. strain can be used. As DNA sequences for amplification and/or expression in Kurthia sp. any DNA sequence of the present invention can be used, but the DNA sequence corresponding to the bioB gene coding for biotin synthase is prefered. One example of such a hybrid plasmid is pYK114 shown in FIG. 14. In this plasmid the bioB gene is under the control of the promoter for the bioH gene and carries the replicating origin of pUB110.

Kurthia sp. 538-51F9 may be transformed with pYK114 obtained as described above by the protoplast transformation method [Molecular Biological Methods for Bacillus, 150, (1990)]. However, since Kurthia sp. 538-51F9 has a low efficiency of regeneration from protoplasts, transformation efficiency of this strain is very low. Therefore, it is preferred to use a strain having high efficiency of regeneration from protoplasts should be used, e.g., Kurthia sp. 538-51F9-RG21 which ca be prepared as described in Example 14 of the present case.

The present invention also provides a process for the production of biotin by the cultivation of the thus obtained transformants, and separation and purification of the produced biotin.

Cultivation of the biotin-expressing cells of the present invention can be done by methods known in the art. The culturing conditions are not critical so long as they are sufficient for the expression of biotin by the biotin-expresing cells to occur. A culture medium containing an assimilable carbon source, a digestible nitrogen source, an inorganic salt, and other nutrients necessary for the growth of the biotin-expressing cell can be used. As the carbon source, for example, glucose, fructose, lactose, galactose, sucrose, maltose, starch, dextrin or glycerol may be employed. As the nitrogen source, for example, peptone, soybean powder, corn steep liquor, meat extract, ammonium sulfate, ammonium nitrate, urea or a mixture thereof may be employed. Further, as an inorganic salt, sulfates, hydrochlorides or phosphates of calcium, magnesium, zinc, manganese, cobalt and iron can be employed. And, if necessary, conventional nutrient factors or an antifoaming agent, such as animal oil, vegetable oil or mineral oil can also be added. If the obtained biotin-expressing cell has an antibiotic resistant marker, the respective antibiotic should be supplemented into the medium. The pH of the culture medium may be between 5 to 9, preferably 6 to 8. The cultivation temperature can be 10 to 45° C., preferably 25 to 30° C. The cultivation time can be 1 to 10 days, preferably 2 to 7

The biotin produced under the conditions as described above can easily be isolated from the culture medium by methods known in the art. Thus, for example, after solid materials have been removed from the culture medium by filtration, the biotin in the filtrate may be absorbed on active carbon, then eluted and purified further with an ion exchange resin. Alternatively, the filtrate may be applied directly to an ion exchange resin and, after the elution, the biotin is recrystallized from a mixture of alcohol and water.

EXAMPLES Example 1 Cloning bioB and bioF Genes of Kurthia sp. 538-KA26.

1. Preparation of the Genomic Library.

The acidomycin-resistant strain of Kurthia sp., 538-KA26 (DSM No. 10609), was cultivated in 100 ml of nutrient broth (Kyokuto Seiyaku Co; Honcho 3-1-1, Nihonbashi, Chuoh-Ku, Tokyo, Japan) at 30° C. overnight, and bacterial cells were recovered by centrifugation. The whole DNA was extracted from the bacterial cells by the phenol extraction method [Experiments with gene fusions, Cold Spring Harbor Laboratory, 137-138, (1984)], and 1.9 mg of the whole DNA was obtained.

The whole DNA (10 μg) was partially digested with 1.2 units of Sau3AI at 37° C. for 1 hour to yield fragments with around 10 Kb in length. 5-15 Kb DNA fragments were obtained by agarose gel electrophoresis.

The vector pBR322 (Takara Shuzo Co.) was completely digested with BamHI, and then treated with alkaline phosphatase to avoid self ligation. The DNA fragments were ligated with the cleaved pBR322 using a DNA ligation Kit (Takara Shuzo Co.) according to the instruction of the manufacturer. The ligation mixture was transferred to Escherichia coli JM109 (Takara Shuzo Co.) by the competent cell method [Molecular Cloning, Cold Spring Harbor Laboratory, 252-253, (1982)], and the strains were selected for ampicillin resistance (100 μg/ml) on agar plate LB medium (1% Bacto-tryptone, 0.5% Bacto-yeast extract, 0.5% NaCl, pH 7.5). About 5,000 individual clones having the genomic DNA fragments were obtained as a genomic library.

The ampicillin-resistant strains of the genomic library of Kurthia sp. 538-KA26 were cultivated at 37° C. overnight in 50 ml of LB medium containing 100 μg/ml ampicillin, and bacterial cells were collected by centrifugation. Plasmid DNA was extracted from the bacterial cells by the alkaline-denaturation method [Molecular Cloning, Cold Spring Harbor Laboratory, 90-91, (1982)].

2. Selection of the Clone Carrying the bioB Gene from the Genomic Library.

The plasmid DNA was transferred by the competent cell method into Escherichia coli bioB deficient mutant R875 (J. Bacteriol. 112, 830-839, 1972) without a biotin synthetase activity. The transformed Escherichia coli R875 cells were washed twice with 0.85% NaCl and streaked on 1.5% agar plates of M9CT medium (0.6% Na₂HPO₄, 0.3% HK₂PO₄, 0.05% NaCl, 0.1% NH₄Cl, 2 mM MgSO₄, 0.1 mM CaCl₂, 0.2% glucose, 0.6% vitamin-free casamino acid, 1 μg/ml thiamin) containing 100 μg/ml of ampicillin, and the plates were incubated at 37° C. for 40 hours. One transformant with the phenotype of the biotin prototrophy was obtained. The transformant was cultivated in LB medium containing 100 μg/ml ampicillin, and the hybrid plasmid was extracted from the cells. The hybrid plasmid carries an insert of 5.58 Kb and was designated pKB100. The restriction map is shown in FIGS. 1 and 2.

3. Complementation of Biotin Deficient Mutants of Escherichia coli with pKB100.

pKB100 was transferred to biotin deficient mutants of Escherichia coli, R875 (bioB⁻), W602 (bioA⁻), R878 (bioC⁻), R877 (bioD⁻), R874 (bioF⁻) or BM7086 (bioH⁻) [J. Bacteriol., 112, 830-839, (1972) and J. Bacteriol., 143, 789-800, (1980)], by the competent cell method. The transformed mutants were washed with 0.85% NaCl three times and plated on M9CT agar plates containing 100 μg/ml of ampicillin and 0.1 ng/ml biotin, and the plates were incubated at 37° C. overnight. Colonies on the plates were replicated on M9CT agar plates with 100 μg/ml ampicillin in the presence or absence of 0.1 ng/ml biotin, the plates were incubated at 37° C. for 24 hours to perform the complementation analysis. As shown in Table 1, the pKB100 could complement not only the bioB but also the bioF mutant. In contrast, bioA, bioC, bioD and bioH mutants were not complemented by pKB100. From this results, it was confirmed that the pKB100 carried the bioB and bioF genes of Kurthia sp. 538-KA26.

TABLE 1 Escherichia coli biotin deficient mutant Plasmid bioA⁻ bioB⁻ bioC⁻ bioD⁻ bioF⁻ bioH⁻ pKB100 − + − − + − pKB200 − + − + − − pKB300 + pKH100 − − − − − + pKC100 − − + − + +

Example 2 Isolation of Hybrid Plasmid Carrying of the bioD Gene of Kurthia sp. 538-KA26.

1. Isolation of the Hybrid Plasmid Carrying the bioD Gene.

The genomic library of Kurthia sp. 538-KA26 of Example 1-1 Was transferred into the Escherichia coli bioD deficient mutant R877, and transformants having an ampicillin resistance and biotin prototrophy phenotype were selected in the same manner as described in Example 1-2. The transformant were cultivated at 37° C. overnight in LB medium with 100 μg/ml ampicillin, and the bacterial cells were collected by centrifugation. The hybrid plasmid was extracted from the cells by the alkaline-denaturation method. The hybrid plasmid had a 7.87 Kb insert DNA fragment and was designated pKB200. Cleavage patterns of pKB200 were analyzed using various restriction endonucleases (HindIII, NcoI, EcoRI, BglII, SalI, and PstI) and compared with that of pKB100. Restriction endonuclease analysis revealed that the two hybrid plasmids had exactly the same cleavage sites and that the 1.5 Kb DNA fragment was extended to the left side of pKB100 and the 0.8 Kb fragment was stretched out to the right side in the pKB200 (FIGS. 1 and 3).

2. Complementation of Biotin Deficient Mutant of Escherichia coli with pKB200.

The pKB200 was transferred to the biotin deficient mutants of Escherichia coli, R875 (bioB⁻), W602 (bioA⁻), R878 (bioC⁻), R877 (bioD⁻), R874 (bioF⁻) or BM 7086 (bioH⁻). Complementation analysis was performed by the method described in Example 1-3. The pKB200 complemented the bioD and bioB mutants, but not the bioA, bioC, bioF and bioH mutants as shown in Table 1. Although the pKB200 overlapped on the whole length of pKB100, pKB200 did not complement the bioF mutant.

Example 3 Isolation of the Hybrid Plasmid Carrying the bioH Gene of Kurthia sp. 538-KA26.

1. Isolation of the Hybrid Plasmid Carrying the bioH Gene.

The genomic library of Kurthia sp. 538-KA26 of Example 1-1 was transferred to the Escherichia coli bioH deficient mutant BM7086. Transformants having the bioH clone were selected for biotin prototrophy in the same manner as in Example 1-2. The hybrid plasmid were extracted from the transformed cells by the alkaline-denaturation method and analyzed by restriction enzymes. The hybrid plasmid had 1.91 Kb inserted DNA fragment and was designated pKH100. Since the genomic library used above has 5-15 Kb of the genomic DNA fragments, the pKH100 was thought to be subjected to a modification, such as deletion, in Escherichia coli strain. The restriction map of the pKH100 is shown in FIGS. 4 and 5. Cleavage patterns of the pKH100 were completely different from those of pKB100 and pKB200. Therefore, pKH100 carried a DNA fragment of the Kurthia chromosome which differed from those in pKB100 and pKB200.

2. Complementation of the Biotin Deficient Mutant of Escherichia coli with pKH100.

Complementation analysis was performed by the method described in Example 1-3. The pKH100 was transferred to the biotin deficient mutants of Escherichia coli, R875 (bioB⁻), W602 (bioA⁻), R878 (bioC⁻), R877 (bioD⁻), R874 (bioF⁻) or BM7086 (bioH⁻). pKH100 complemented only the bioH mutant, but not the bioB, bioA, bioC, bioD and bioF mutants as shown in Table 1. Thus, pKH100 carries the bioH gene.

Example 4 Isolation of the Hybrid Plasmid Carrying the bioC Gene of Kurthia sp. 538-KA26.

1. Isolation of the Hybrid Plasmid Carrying the bioC Gene.

The genomic library of Kurthia sp. 538-KA26 of Example 1-1 was transferred to the Escherichia coli bioC deficient mutant R878. Transformants with the bioC clone were selected for biotin prototrophy in the same manner as described in Example 1-2. The hybrid plasmid was extracted from the transformant cells by the alkaline-denaturation method and analyzed with restriction enzymes. The hybrid plasmid had a 6.76 Kb inserted DNA fragment and was designated pKC100. The restriction map of pKC100 is shown in FIGS. 6 and 7. Cleavage patterns of pKC100 were completely different from those of pKB100, pKB200 and pKH100. Therefore, pKC100 carries a different region of the Kurthia chromosome from those of pKB100, pKB200 and pKH100.

2. Complementation of the Biotin Deficient Mutant of Escherichia coli with pKC100.

The complementation analysis was performed by the method described in Example 1-3. pKC100 was transferred to the biotin deficient mutants of Escherichia coli, R875 (bioB⁻), W602 (bioA⁻), R878 (bioC⁻), R877 (bioD⁻), R874 (bioF⁻) or BM7086 (bioH⁻). pKC100 complemented the bioC, bioF and bioH mutants as shown in Table 1. Since the inserted DNA fragment in pKH100 was different from those in pKB100 and pKH100, pKC100 carried not only the bioC gene but also genes for isozymes of the bioF gene product (KAPA synthetase) and the bioH gene product.

Example 5 Isolation of the Hybrid Plasmid Carrying the bioA Gene of Kurthia sp. 538-KA26.

1. Isolation of the Left Region of the Chromosomal DNA in pKB200.

We isolated the left region of the chromosomal DNA in pKB200 from Kurthia sp. 538-KA26 chromosomal DNA by the hybridization method. The whole DNA of Kurthia sp. 538-KA26 was completely digested with HindIII and subjected to agarose gel electrophoresis. The DNA fragments on the gel were denatured and then transferred to a nylon membrane (Hybond-N, Amersham) according to the recommendations of the manufacturer.

pKB200 was completely digested with NcoI, and a 2.1 Kb NcoI fragment was isolated by agarose gel electrophoresis (FIG. 1). The NcoI fragment was labeled with ³²P by the Multiprime DNA labeling system (Amersham) and used as a hybridization probe. The hybridization was performed on the membrane prepared above using the “Rapid hybridization buffer” (Amersham) according to the instructions of the manufacturer. The probe strongly hybridized to a HindIII fragment of about 8.5 Kb.

In order to isolate the 8.5 Kb fragment, the whole DNA of Kurthia sp. 538-KA26 was completely digested with HindIII, and 7.5-9.5 Kb DNA fragments were obtained by agarose gel electrophoresis. The vector plasmid pUC19 (Takara Shuzo Co.) was completely digested with HindIII and treated with alkaline phosphatase to avoid self ligation. The 7.5-9.5 Kb DNA fragments were ligated with the cleaved the pUC19 using a DNA ligation Kit (Takara Shuzo Co.), and the reaction mixture was transferred to Escherichia coli JM109 by the competent cell method. About 1,000 individual clones carrying such genomic DNA fragments were obtained as a genomic library.

The selection was carried out by the colony hybridization method according to the protocol described by Maniatis et al. [Molecular Cloning, Cold Spring Harbor Laboratory, 312-328, (1982)]. The grown colonies on the agar plates were transferred to nylon membranes (Hybond-N, Amersham) and lysed by alkali. The denatured DNA was immobilized on the membranes. ³²P labeled NcoI fragments prepared as described above were used as a hybridization probe, and the hybridization was performed using the “Rapid hybridization buffer” (Amersham) according to the instructions of the manufacturer. Three colonies which hybridized with the probe DNA were obtained, and hybrid plasmids in these colonies were extracted by the alkaline-denaturation method.

The structure analysis was performed with restriction enzymes (BamHI, HindIII, NcoI, EcoRI, BglII, SalI and PstI). All of the three hybrid plasmids had a 8.44 Kb inserted DNA fragment, and the three hybrid plasmids had exactly the same cleavage patterns. These results indicated that they were identical. This hybrid plasmid was designated pKB300. The restriction map of pKB300 is shown in FIG. 1. About half length of the genomic DNA fragment in pKB300 overlappes with that of pKB200.

2. Complementation of the bioA Deficient Mutant of Escherichia coli with pKB300.

The complementation analysis of Escherichia coli W602 (bioA⁻) with pKB300 was performed by the method described in Example 1-3. Since pKB300 complemented the bioA mutation (Table 1), pKB300 carries the bioA gene of Kurthia sp.

Example 6 Subcloning of the bioA, B, D and F Genes of Kurthia sp. 538-KA26.

1. Construction of the Hybrid Plasmid pKB103 and pKB104.

pKB100 was completely digested with HindIII, and a 3.3 Kb HindIII fragment was isolated. The 3.3 Kb fragment was ligated with the vector pUC18 (Takara Shuzo Co.) cleaved with HindIII using a DNA ligation Kit to construct the hybrid plasmids pKB103 and pKB104. In pKB103 and pKB104, the 3.3 Kb fragments were inserted in both orientations relative to the promoter-operator of the lac gene in pUC18. Their restriction map is shown in FIG. 8.

Complementation of the bioB or bioF deficient mutants of Escherichia coli (R875 or R874) were performed with pKB103 and pKB104 in the same manner as described in Example 1-3. pKB103 and pKB104 complemented the bioB and bioF mutants (Table 2).

2. Construction of Derivatives of pKB200.

Since pKB200 complemented the bioD mutation and covered the whole length of pKB100 carrying the bioB and bioF genes, a series of deletion mutations of pKB200 were constructed to localize more precisely bioB, bioD and bioF. A 4.0 Kb SalI-HindIII fragment of pKB200 was inserted into the SalI and HindIII sites of pUC18 and pUC19 to give pKB221 and pKB222 in which the SalI-HindIII fragment is placed in both orientations.

pKB200 was completely digested with NruI, and a 7.5 Kb NruI fragment was isolated by agarose gel electrophoresis. The NruI fragment was recirculated by the DNA ligation Kit, and pKB223 was obtained.

pKB200 was completely digested with HindIII. A 4.8 Kb HindIII fragment was isolated by agarose gel electrophoresis and cloned into the HindIII site of pUC18 in both orientations to generate pKB224 and pKB225.

pKB200 was partially digested with NcoI, and a 3.1 Kb NcoI fragment was isolated by agarose gel electrophoresis. The ends of the NcoI fragment were made blunt by using the Klenow fragment of the DNA polymerase I (Takara Shuzo Co.) and ligated with HindIII linker (Takara Shuzo Co.) The 3.1 Kb HindIII fragment was obtained by treatment with HindIII and cloned into the HindIII site of the pUC19 in both orientation to give pKB228 and pKB229.

In the same manner, both ends of a 2.1 Kb NcoI fragment of pKB200 were converted to HindIII sites by treatment with the Klenow fragment and addition of HindIII linkers. Then the obtained HindIII fragment was inserted into the HindIII site of pUC19 in both orientations to give pKB230 and pKB231.

pKB234 and pKB235 were generated by insertion of a 1.6 Kb HindIII-NruI fragment of pKB230 into the HindIII and SmaI sites of pUC19 and pUC18, respectively.

The restriction maps of the pKB200 derivatives are shown in FIG. 8.

3. Complementation Analysis of Biotin Deficient Mutants of Escherichia coli with pKB200 Derivatives.

Complementation analysis was performed with the pKB200 derivatives in the same manner as described in Example 1-3. The complementation results are summarized in Table 2. The bioB deficient mutant was complemented by pKB221, pKB222, pKB224 and pKB225, but not by pKB223, pKB228, pKB229, pKB230, pKB231, pKB234 and pKB235. The bioF deficient mutant was complemented by pKB223, pKB224, pKB225, pKB228 and pKB229, but not by pKB221, pKB222, pKB230, pKB231, pKB234 and pKB235. On the other hand, the bioD deficient mutant was complemented by pKB223, pKB224 and pKB225, but not by pKB221 and pKB222.

Together with the complementation analysis with pKB103 and pKB104, these results support that the bioF gene is present at the left side of the first NruI site on pKB103 while the bioB gene is located on the right side of the same NruI site with a short overlap to the left and that the bioD gene is present on at most 1.5 Kb left side region of the pKB200. Thus, the complementation results with various derivatives of pKB100 and pKB200 showed that the bioD, bioF and bioB genes lie in turn on the 4.4 Kb region at the left side of the HindIII site of pKB200.

4. Construction of the Hybrid Plasmid pKB361.

To determine the location of the bioA gene, the derivative of pKB300 was constructed. pKB361 was generated by insertion of a 2.8 Kb BamHI-SalI fragment of pKB300 into the BamHI and SalI sites of pUC19 (FIG. 8).

pKB361 was transferred to the bioA deficient mutant of Escherichia coli (W602), and complementation analysis was performed in the same manner as described in Example 1-3. The bioA mutant was complemented by pKB361 (Table 2), suggesting the presence of the bioA gene within the 2.8 Kb region between the BamHI and SalI sites of pKB300.

TABLE 2 Escherichia coli biotin deficient mutant Plasmid bioA⁻ bioD⁻ bioF⁻ bioB⁻ pKB103, 104 + + pKB221, 222 − − + pKB223 + + − pKB224, 225 + + + pKB228, 229 + − pKB230, 231 − − pKB234, 235 − − pKB361 +

Example 7 Subcloning of the bioH Gene of Kurthia sp. 538-KA26

1. Construction of the Hybrid Plasmids pKH101 and pKH102.

pKH100 was completely digested with BamHI and recirculated with a DNA ligation Kit to generate pKH101 in which a 0.75 Kb BamHI fragment was deleted from pKH100 (FIG. 4). pKH102 was constructed from pKH100 by treatment with HindIII followed by recirculation with a DNA ligation Kit. The pKH102 lacked a 1.07 Kb HindIII fragment in pKH100 (FIG. 4).

Complementation analysis of the Escherichia coli bioH mutant (R878) was performed with pKH101 and pKH102 in the same manner as in Example 1-3. pKH101 complemented the bioH mutant, but not pKH102 (FIG. 4). This result indicated that the bioH gene is located in the left region (1.16 Kb) of the BamHI site on pKH100.

Example 8 Subcloning of the bioC Gene of Kurthia sp. 538-KA26

pKC100 was completely digested with BamHI, and a 1.81 Kb BamHI fragment was isolated by agarose gel electrophoresis. The BamHI fragment was ligated with pBR322 treated with BamHI and the Klenow fragment by a DNA ligation Kit. Finally, pKC101 and pKC102 in which the BamHI fragment was inserted in both orientations were obtained (FIG. 6).

pKC101 and pKC102 were transferred to the Escherichia coli bioC mutant R878, and complementation analysis was carried out in the same manner as in Example 1-3. The bioC mutant was complemented with pKC101 and pKC102, and the bioC gene was confirmed to lie in the 1.81 Kb BamHI fragment.

Example 9 Nucleotide Sequence of the Inserted DNA Fragments on pKB100, pKB200 and pKB300.

For nucleotide sequencing analysis of the inserted DNA fragments of pKB100, pKB200 and pKB300, several subclones overlapping mutually were constructed using pUC18, pUC19, M13mp18 and M13mp19 (Takara Shuzo Co.) and a series of deletion derivatives of the subclones were obtained by the Kilo-Sequencing Deletion Kit (Takara Shuzo Co.). Then, nucleotide sequencing analysis of the deletion derivatives was carried out by the dideoxy-chain termination technique (Sequenase version 2.0 DNA sequencing kit using 7-deaza-dGTP, United States Biochemical Co.). The results were analyzed by the computer program (GENETYX) from Software Development Co.

Computer analysis of this sequence revealed that the cloned DNA fragment has the capacity to code for six open reading frames (ORF). This gene operon has two gene clusters proceeding to both directions (FIG. 9-A).

The first ORF in the left gene cluster starts with the TTG codon preceded by a ribosomal binding site (RBS) with homology to the 3′ end of the Bacillus subtilis 16S rRNA and codes for a protein of 194 amino acid residues having a molecular weight of 21,516. It was not possible to determine the function of the gene product by the complementation analysis, accordingly, this ORF was named ORF1.

The nucleotide sequence of the second ORF in the left gene cluster is shown in SEQ ID NO: 1. This gene codes for a protein of 236 amino acid residues with a molecular weight of 26,642. The predicted amino acid sequence of this gene product is shown in SEQ ID NO: 2. A putative RBS is found upstream of the ATG initiation codon. The complementation analysis (Example 6-3) showed that this ORF is the bioD gene.

The third ORF in the left gene cluster has a putative RBS upstream of the ATG initiation codon, and the nucleotide sequence of this gene is shown in SEQ ID NO: 3. This gene codes for a protein of 460 amino acid residues with a molecular weight of 51,731. The predicted amino acid sequence of this gene product is shown in SEQ ED NO: 4. This ORF was confirmed to correspond to the bioA gene (Example 6-3). An inverted repeat sequence was found to be located approximately 3 bp downstream from the termination codon. This structure may act as a transcriptional terminator.

The first ORF in the right gene cluster, named ORF2 starts at the ATG codon preceded by a putative RBS. This gene product is a protein consisting of 63 amino acid residues, and the calculated molecular weight is 7,447. We could not identify the function of this gene product by the complementation analysis and the amino acid sequence homology search. Accordingly, this ORF was named ORF2.

The nucleotide sequence of the second ORF in the right gene cluster is shown in SEQ ID NO: 5. This gene has three potential ATG initiation codons corresponding to the first, twenty-fifth and thirty-second amino acid residues. The complementation analysis (Example 6-3) showed that this ORF corresponds to the bioF gene. The predicted amino acid sequence of this gene product is shown in SEQ ID NO: 6. The molecular weight of the predicted protein with 387 amino acid residues was calculated to be 42,619, starting from the first initiation codon.

The third ORF in the right gene cluster as shown in SEQ ID NO: 7 has three potential initiation codons, two ATG codons (the first and eighteenth amino acid residues) and a GTG codon (the twelfth amino acid residue). The predicted amino acid sequence of this gene product is shown in SEQ ID NO: 8. The molecular weight of the predicted protein with 338 amino acid residues translated from the first initiation codon was calculated to be 37,438. The complementation analysis (Example 6-3) showed that this ORF corresponds to the bioB gene. The presence of an inverted repeat sequence 16 bp downstream from the termination codon is characteristic of a transcriptional terminator.

There were two possible promoter sequences forming face to face promoters between ORF1 and ORF2 as shown in FIG. 10. The transcriptions proceed to the left into the ORF1, bioD and bioA gene cluster, and to the right into the ORF2, bioF and bioB gene cluster. In addition, two transcriptional terminators were located downstream of the termination codons of the bioA and bioB genes. Therefore, the transcriptions in both directions generate two different mRNAs.

Two components of the inverted repeat sequences, Box1 and Box2, were found between the initiation site of the ORF1 and ORF2 genes (FIG. 10). The overall homology for the Box1 and Box2 is 82.5%. Comparison of the Box1 or Box2 with the operator of the Escherichia coli biotin operon [Nature, 276, 689-694, (1978)] showed that there is a high level of conservation (54.6% homology for both). The similarities between two inverted repeat sequences of the biotin operator of Escherichia coli suggest that the Box1 and Box2 must be involved in the negative control of the biotin synthesis by biotin.

Example 10 Nucleotide Sequence of the Inserted DNA Fragments of pKH100.

The nucleotide sequence analysis of the inserted DNA fragment of pKH100 was performed in the same manner as described in Example 9. A gene cluster containing two ORFs was found on the inserted DNA fragment (FIG. 9-B). In addition, it was confirmed that a part of the vector plasmid pBR322 and the inserted DNA fragment were deleted.

The first ORF as shown in SEQ D NO: 9 codes for a protein of 267 amino acid residues, and the calculated molecular weight is 29,423. The predicted amino acid sequence of this gene product is shown in SEQ ID NO: 10. A putative RBS is located at 6 bp upstream from the ATG initiation codon. The complementation analysis, as shown in Example 7, indicated that this ORF corresponds to the bioH gene.

The second ORF with a potential RBS was found downstream of the bioH gene. The ORF codes for a protein of 86 amino acid residues with a molecular weight of 9,955. The protein encoded by the ORF did not share homology with the biotin gene products of Escherichia coli and Bacillus sphaericus. The ORF was named ORF3.

A possible promoter sequence was found upstream from the initiation codon of the bioH gene as shown in FIG. 11. Since no inverted repeat sequence such as Box1 and Box2 was found in the 5′-noncoding region of the bioH gene, the transcription of this gene cluster must be not regulated. In addition, there is ah inverted repeat sequence overlapping with the termination codon of ORF3. Since this structure is able to act as a transcriptional terminator, the putative bioH promoter would therefore allow transcription of the bioH and ORF3 genes.

Example 11 Nucleotide Sequence of the Inserted DNA Fragments of pKC100.

The nucleotide sequence analysis of the inserted DNA fragment of pKC100 was performed in the same manner as described in Example 9. A gene cluster consisting of three ORFs was found on the inserted DNA fragment (FIG. 9-C).

The third ORF has a putative RBS upstream of the initiation codon and the nucleotide sequence of this gene is shown in SEQ ID NO: 15. This gene codes for a protein of 276 amino acid residues, and the calculated molecular weight is 31,599. The predicted amino acid sequence of this gene product is shown in SEQ ID NO: 16. The complementation analysis as shown in Example 8 indicating that this ORF corresponds to the bioC gene.

The first ORF as shown in SEQ ID NO: 11 codes for a protein of 398 amino acid residues with a molecular weight of 44,776. A putative RBS is located upstream of the initiation codon. The predicted amino acid sequence of this gene product as shown in SEQ ID NO: 12 has 43.0% homology with that of the bioF gene product of Kurthia sp. 538-KA26 in Example 9. Moreover, the pKC100 complemented the Escherichia coli bioF mutant as shown in Example 4. Therefore, this ORF was concluded to be a gene for an isozyme of the bioF gene product, KAPA synthetase. Therefore, this ORF was named bioFII gene.

The second ORF as shown in SEQ ID NO: 13 has a putative RBS upstream of the initiation codon. This gene codes for a protein of 248 amino acid residues with a molecular weight of 28,629. The predicted amino acid sequence of this gene product as shown in SEQ ID NO: 14 has 24.2% homology with that of the bioH gene product of Kurthia sp. 538-KA26 in Example 10. As shown in Example 4, the pKC100 also complemented the Escherichia coli bioH mutant. These results showed that this ORF is a gene for isozyme of the bioH gene product therefore this ORF was named bioHII gene.

A possible promoter sequence was found upstream from the initiation codon of the bioFII gene as shown in FIG. 12. An inverted sequence is located between the promoter sequence and the RBS of the bioFII gene. This inverted repeat sequence designated Box3 was compared with the Box1 and Box2 located between the ORF1 and ORF2 genes (Example 9). The Box1, Box2 and Box3 were extremely similar to each other (homology of Box1 and Box3 was 80.0% and that of Box2 and Box3 was 77.5%). Therefore, the cluster of the bioC gene must be regulated by a negative control similarly to the bioA cluster and the bioB cluster. In addition, there is an inverted repeat sequence 254 bp downstream of the termination codon of the bioC gene. This structure is thought to act as a transcriptional terminator.

Example 12 Construction of the Shuttle Vector for Escherichia coli and Kurthia sp. Strain

A shuttle vector for Escherichia coli and Kurthia sp. was constructed by the strategy as shown in FIG. 13. The Staphylococcus aureus plasmid pUB110 (Bacillus Genetic Stock Center; The Ohio State University, Department of Biochemistry, 484 West Twelfth Avenue, Columbus, Ohio 43210, USA) was completely digested with EcoRI and PvuII. A 3.5 Kb EcoRI-PvuII fragment containing the replication origin for Kurthia sp. and the kanamycin resistant gene was isolated by agarose gel electrophoresis. The pUC19 was completely digested with EcoRI and DraI, and the 1.2 Kb EcoRI-DraI fragment having the replication origin of Escherichia coli was isolated by agarose gel electrophoresis. Then, these fragments were ligated with a DNA ligation Kit to generate the shuttle vector pYK1. pYK1 can replicate in Escherichia coli and Kurthia sp., and Escherichia coli or Kurthia sp. transformed by pYK1 show resistance to kanamycin.

Example 13 Construction of the Expression Plasmid of the bioB Gene of Kurthia sp.

pYK114 in which the Kurthia bioB gene was inserted downstream of the promoter of the Kurthia bioH gene was constructed by the strategy as shown in FIG. 14. pKH101 of Example 7 was completely digested with BanII, and ends of BanII fragments were blunted by the Klenow fragment of the DNA polymerase. Then the BanII fragments were treated with EcoRI, and a 0.6 Kb EcoRI-blunt fragment containing the bioH promoter was isolated by agarose gel electrophoresis. pKB104 of Example 6 was completely digested with KpnI, and KpnI ends were changed to blunt ends by treatment with the Klenow fragment. After digestion with HindIII, a 1.3 Kb blunt-HindIII fragment carrying the bioB gene was isolated by agarose electrophoresis. The EcoRI-blunt and blunt-HindIII fragments were ligated with pYK1 digested with EcoRI and HindIII to construct pYK114. The bioB gene is constitutively expressed under the bioH promoter from pYK114.

Example 14 Isolation of the Derivative Strain of Kurthia sp. 538-51F9 with a High Transformation Efficiency

Kurthia sp. 538-51F9 (DSM No.10610) was cultivated at 28° C. in 50 ml of Tripticase Soy Broth (Becton Dickinson) until an optical density at 600 mn (OD₆₀₀) of 1.0. Grown cells were collected by centrifugation and suspended in SMM (0.5 M sucrose, 0.02M sodium maleate, 0.02 M MgCl₂ 6H₂O; pH 6.5) at OD₆₀₀ 16. Then lysozyme (Sigma) was added to the cell suspension at 200 mg/ml, and the suspension was incubated at 30° C. for 90 minutes to form protoplasts. After the protoplasts have been washed with SMM twice, they were suspended in 0.5 ml of SMM. 1.5 ml of PEG solution (30% w/v polyethyleneglycol 4000 in SMM) was added to the protoplast suspension, and the suspension was incubated for 2 minutes on ice. Then 6 ml of SMM was added, and the protoplasts were collected by centrifugation. The collected protoplasts were suspended in SMM and incubated at 30° C. for 90 minutes. DM3 medium (0.5 M sodium succinate pH 7.3, 0.5% w/v casamino acid, 0.5% w/v yeast extract, 0.3% w/v KH₂PO₄, 0.7% w/v K₂HPO₄, 0.5% w/v glucose, 0.02 M MgCl₂ 6H₂O, 0.01w/v bovine serum albumin) containing 0.6% agarose (Sigma; Type VII) was added to the protoplast suspension, and the suspension was overlaid on DM3 medium agar plates. The plates were incubated at 30° C. for 3 days. In total, 65 colonies regenerated on the DM3 plates were obtained.

The transformation efficiency of the regenerated strains was investigated with pYK1 of Example 12. As a result, 40 strains were selected and cultivated at 28° C. in 50 ml of Tripticase Soy Broth until OD₆₀₀ was 1.0. Grown cells were collected by centrifugation and suspended in SMM at OD₆₀₀ 16. Then the cells were treated with lysozyme by the method described above, and the protoplasts were obtained. The protoplasts were suspended in 0.5 ml SMM, and PYK1 (1 μg) was added to the protoplast suspensions. After addition of 1.5 ml of a PEG solution, the suspensions were incubated for 2 minutes on ice. 6 ml of SMM was added, and the protoplasts were collected by centrifugation. Then the protoplasts were suspended in SMM and incubated at 30° C. for 90 minutes. The DM3 medium containing 0.6% agarose was added to the protoplast suspensions, and the suspensions were overlaid on DM3 medium agar plates. The plates were incubated at 30° C. for 3 days. The DM3-agarose including the regenerated colonies on the plates were collected and spread on the nutrient broth agar plates with 5 μg/ml kanamycin to select the transformants. The plates were incubated overnight at 30° C. Finally, the derivative strain, Kurthia sp. 538-51F9-RG21, characterized by a high transformation efficiency (2,000 transformants per μg of DNA) was obtained.

Example 15 Amplification of the bioB Gene in Kurthia sp. 538-51F9-RG21

1. Transformation of Kurthia sp. 538-51F9-RG21.

The expression plasmid of the bioB gene of the Kurthia strain, pYK114, was constructed as described in Example 13. Kurthia sp. 538-51F9-RG21 was transformed with pYK114 and the vector plasmid pYK1 as described in Example 14. Kurthia sp. 538-51F9-RG21 carrying pYK1 or pYK114 was named Kurthia sp. 538-51F9-RG21 (pYK1) or Kurt sp. 538-51F9-RG21 (pYK114), respectively.

2. Biotin Production by Fermentation.

Kurthia sp. 538-51F9-RG21 (pYK1) and Kurthia sp 5351.F9-RG21-(pY-K114) were inoculated into 50 ml of the production medium (6% glycerol, 5.5% proteose peptone, 0.1% KH₂PO₄, 0.05% MgSO₄ 7H₂O, 0.05% FeSO₄ 7H₂O, 0.001% MnSO₄ 5H₂O; pH 7.0) containing 5 μg/ml kanamycin. As a control, Kurthia sp. 538-51F9-RG21 was inoculated into 50 ml of the production medium. The cultivation was carried out at 28° C. for 120 hours.

After the cultivation, 2 ml of the culture broth was centrifuged to remove bacterial cells, and the supernatant was obtained. Biotin production in the supernatant was assayed by the microbiological assay using Lactobacillus plantarum (ATCC 8014). The amounts of produced biotin are given in Table 3.

TABLE 3 Strain of Kurthia sp. Biotin production (mg/L) 51F9-RG21 15.4 51F9-RG21 (pYK1) 14.3 51F9-RG21 (pYK114) 39.0 

1. An isolated DNA molecule comprising a polynucleotide selected from the group consisting of: a) SEQ ID NO: 7; b) a polynucleotide which encodes the polypeptide of SEQ ID NO: 8; and c) a polynucleotide which hybridizes to the complement of the polynucleotide from a) or b) under stringent hybridizing conditions, wherein the stringent conditions include hybridizing and washing in 0.2×SSC at about 65° C. and wherein the polynucleotide encodes a polypeptide having biotin synthase activity.
 2. The isolated DNA molecule of claim 1 which comprises SEQ ID NO:
 7. 3. An expression vector comprising a polynucleotide selected from the group consisting of: a) SEQ ID NO: 7; b) a polynucleotide which encodes the polypeptide of SEQ ID NO: 8; and c) a polynucleotide which hybridizes to the complement of the polynucleotide from a) or b) under stringent hybridizing conditions, wherein the stringent conditions include hybridizing and washing in 0.2×SSC at about 65° C. and wherein the polynucleotide encodes a polypeptide having biotin synthase activity.
 4. The expression vector of claim 3 which comprises SEQ ID NO:
 7. 5. A biotin-expressing cell transformed with an expression vector comprising polynucleotide selected from the group consisting of: a) SEQ ID NO: 7; b) a polynucleotide which encodes the polypeptide of SEQ ID NO: 8; and c) a polynucleotide which hybridizes to the complement of the polynucleotide from a) or b) under stringent hybridizing conditions, wherein the stringent conditions include hybridizing and washing in 0.2×SSC at about 65° C. and wherein the polynucleotide encodes a polypeptide having biotin synthase activity.
 6. The cell of claim 5 in which the expression vector comprises SEQ ID NO:
 7. 7. A process for the production of biotin comprising culturing a biotin-expressing cell transformed by an expression vector, wherein the expression vector comprises a polynucleotide selected from the group consisting of: a) SEQ ID NO: 7; b) a polynucleotide which encodes the polypeptide of SEQ ID NO: 8; and c) a polynucleotide which hybridizes to the complement of the polynucleotide from a) or b) under stringent hybridizing conditions, wherein the stringent conditions include hybridizing and washing in 0.2×SSC at about 65° C. and wherein the polynucleotide encodes a polypeptide having biotin synthase activity.
 8. The process of claim 7 in which the expression vector comprises SEQ ID NO:
 7. 